Is there a formula to figure out how many square feet my 2-ton split a/c will cool?

Question

I am renovating my attic and need to know whether or not to purchase a secondary unit. I am adding 600 ft/sq, BUT the ceiling is arched due to the roof, so the cubic footage is somewhat less.

Answer 1

Yep, 500 feet for average insulation and 700 feet for high end  well insulated houses.

You may be better off just getting an 18,000 btu heat and cool unit at Lowe's or the Depot. Just permanent mount it and make sure you have good drainage.

I added a window to put one in a house by building a dormer on the back side where it did not hurt the curb appeal. Extra light was a nice addition too.

Answer 2

It depends on a lot of things.  If you do a really good job airsealing and insulating the new space and do some airsealing around the rest of your house, you won't need as much cooling capacity.  You could easily get 600-800 sq ft per ton if you tighten your house up a bit.  It'll cut down on your energy bills too.

Answer 3

12000BTUs = 1 ton. You will need at least a ton added to cool this space, maybe a little more since your in an attic. Heat rises, so the attic is the hottest space in the home.

http://www.fedders.com/BTUsizing.htm

Answer 4

A general rule is 1 ton for every 500 to 700 sq. ft. of space.

  Certainly in your case the issue may vary depending on the insulation, etc.

   We also have no idea how much space your two ton is working in now.